1. Field of the Invention
The present invention relates generally to an apparatus and method for chamfering a wafer, and more particularly to an apparatus and method for chamfering a periphery of a wafer.
2. Description of Related Art
A silicon ingot is sliced by a slicing machine into wafers, which are used for semiconductor devices. Then, the periphery of each wafer is chamfered in order to prevent the wafer from chipping, cracking, and so on. The wafer is chamfered by pressing a rotating grindstone against the periphery of the rotating wafer. A conventional chamfering apparatus moves the grindstone forward and backward, or vertically and horizontally with respect to the wafer to chamfer the periphery of the wafer.
The conventional chamfering apparatus, however, does not have sufficient stiffness because the grindstone rotates at a high speed during the chamfering, and it vibrates easily. Therefore, the machined surface of the wafer has coin marks, chipping, or the like.
The conventional chamfering apparatus relatively moves the wafer closer to the grindstone, which is rotating at the high speed (at a circumferential speed of 1000-3000 [m/min]). After grinding the wafer by a predetermined amount, the chamfering apparatus rotates the wafer slowly (at a circumferential speed of 0.6-3 [m/min]) to chamfer the whole circumference of the wafer. To reduce the machining time for one wafer, it is necessary to increase the circumferential speed of the wafer. To increase the circumferential speed of the wafer, the rotational speed of the grindstone must be increased, or the grindstone must have a relatively rough mesh. In the case that the rotational speed of the grindstone is increased, if a newly-attached grindstone is not well-balanced, the grindstone vibrates while rotating at a high speed. This causes defects on the machined surface of the wafer (coin marks, chipping, cracks, or the like). On the other hand, in the case that the grindstone has the relatively rough mesh, the grindstone grinds the wafer by a large amount, and thus, the wafer can be badly damaged. To address these problems, the diameter of the wafer is reduced by etching, or the diameter is reduced by gradually chamfering the wafer. These methods, however, require a long time.
In view of the foregoing, it is an object of the present invention to provide an apparatus and method for accurately chamfering the wafer.
To achieve the above-mentioned object, the present invention is directed to a wafer chamfering apparatus for chamfering a periphery of a wafer, comprising: a main grindstone; a main grindstone rotating means for rotating the main grindstone; a wafer table for holding the wafer in parallel with the main grindstone; a wafer table rotating means for rotating the wafer table; and a wafer table moving means for moving the wafer table along an axis of the wafer and moving the wafer table along a face of the wafer; wherein the wafer is rotated while being moved to the main grindstone being rotated, and the periphery of the wafer is brought into contact with the main grindstone so as to be chamfered.
According to the present invention, the main grindstone is rotated at the constant position, and the wafer is moved so that the periphery thereof can come into contact with the main grindstone. The stiffness of the apparatus is improved since the main grindstone is only rotated and not moved. This prevents the vibrations of the main grindstone, which is rotating at a high speed, and improves the accuracy of the machined surface of the wafer.
To achieve the above-mentioned object, the present invention is also directed to a wafer chamfering method, comprising the steps of: rotating a grindstone and a wafer at high speeds; and getting the grindstone and the wafer closer to each other, thereby gradually chamfering a periphery of the wafer by the grindstone.
According to the present invention, both the grindstone and the wafer are rotated at high speeds to thereby increase the machining speed and reduce the machining time. Grinding the periphery of the wafer gradually prevents the damage on the machined surface of the wafer, thus improving the accuracy of the machined surface of the wafer.
To achieve the above-mentioned object, the present invention is also directed to a wafer chamfering method, comprising the steps of: arranging a grindstone and a wafer separately on two parallel straight lines with a predetermined interval; rotating the grindstone and the wafer at high speeds; moving at least one of the wafer and the grindstone on the straight line to bring the grindstone into contact with a periphery of the wafer, thereby gradually chamfering the periphery of the wafer by the grindstone.
According to the present invention, both the grindstone and the wafer are rotated at high speeds to thereby increase the machining speed and reduce the machining time. Grinding the periphery of the wafer gradually prevents the damage on the machined surface of the wafer, thus improving the accuracy of the machined surface of the wafer.
To achieve the above-mentioned object, the present invention is directed to a wafer chamfering method, comprising the steps of: roughly chamfering a periphery of a rotating wafer by a first rotating grindstone with a large diameter by getting the rotating wafer and the first rotating grindstone closer to each other; and finely chamfering the periphery of the rotating wafer by a second rotating grindstone with a small diameter by getting the rotating wafer and the second rotating grindstone closer to each other.
According to the present invention, it is possible to prevent the vibrations of the grindstone during the finely chamfering by using the grindstone with the small diameter. Thus, it is possible to improve the accuracy of the machined surface of the wafer.